This invention relates to the use of surfactents which may be inactivated or degraded upon contact with one or more materials possibly in one or more layers of a substrate. The composite material includes a surfactant that can be applied to a substrate such as a nonwoven web such that the surfactant reduces the surface tension of a fluid so that the fluid intake into the substrate is enhanced and such that the surfactant is inactivated upon contacting or passing into another portion of the substrate.
Surfactants are well-known compounds that are used in many fields to provide low surface tension to water or other fluids resulting in increased wettability, spreadability, emulsification, dispersion, penetration, and/or improved adhesion. Some surfactants also are known to impart softness characteristics to certain products, such as tissue.
While surfactants may produce a number of desired properties and benefits, prior usage of articles containing surfactants or having surfactants on the surface of the substrate reveals that surfactants frequently have adverse effects on the properties of the materials and/or surroundings to which the surfactants pass. For example, a surfactant is most commonly applied to a surface of a substrate in anticipation of fluid contact; however, after the surfactant is contacted by a fluid, some or all of the surfactant typically dissolves in the fluid and flows into the substrate with the fluid. The presence of the surfactant in the fluid in the substrate may result in reduced fluid flow (wicking) through the substrate due to reduced fluid surface tension which reduces capillary pressure. That is, if the substrate contains a surfactant the surfactant will enhance the passage of a contacting fluid into the substrate. However, the presence of the surfactant in the fluid reduces the wicking force (speed) end thus the substrate directly under the liquid penetration point can become saturated. This saturation will restrict the passage of more fluid into the substrate which may result in leakage and, an undesirable appearance of the product or even adverse contact with the skin of the wearer. The presence of a superabsorbent in the substrate magnifies the problem. As the surfactant containing fluid is being wicked at a slower rate, the fluid has a longer residency time near the superabsorbent near the fluid entry location into the substrate. These superabsorbent particles continue to swell and absorb fluid which eventually will lead to xe2x80x9cgel blockingxe2x80x9d. More specifically, the phenomenon of gel blocking describes the tendency of hydrogel materials or so-called xe2x80x9csuperabsorbent materialsxe2x80x9d to swell in place once wetted and produce gelatinous material which blocks further transmission of the fluid being absorbed. The gelatinous material not only effects the fluid intake or absorption properties or the superabsorbent material, but also inhibits the wicking and dispersion properties of the total absorbent material. Therefore, where the fluid being absorbed contacts the absorbent material in a highly localized area at a rate which exceeds that which the super absorbent material can readily tolerate, much of the absorbent medium frequently is not utilized at all, thus resulting in an inefficient product.
Although the use of surfactants provides some of the properties noted above, the use of surfactants may also create additional problems. For example, certain surfactants have been stated by authorities to have potential long-term harmful characteristics, and may give rise to environmental concerns if not inactivated or degraded before being released into the environment. Furthermore, most frequently used surfactants are not readily degradable, and thus remain surface active long after producing the desired effect on the desired surroundings. While the use of non-degradable or not readily degradable surfactants may provide certain desired properties to a substrate (i.e. reduced surface tension, enhanced or controlled penetration and/or softness), because the surfactants may be non-degradable they not only continue to attempt to impart these properties on their surroundings (including those on which it is not intended or is undesirable to do so), but may, according to authorities, also cause damage (i.e. cell destruction) in the environment long after the product incorporating them has been used, discarded and/or destroyed.
In addition to creating and/or causing environmental problems or concerns, surfactants which are not inactivated or degraded, also may produce less than desirable results if used in some products. That is, the surfactants which are not degraded or inactivated continue, at least to some degree, to impart their characteristics on surrounding fluids and surfaces after the surfactant has achieved its purpose for incorporation. For example, a surfactant is unable to distinguish between when it is desired that the surface tension of a fluid be reduced and when it is undesirable to do so. Consequently, unless degraded, inactivated, or otherwise prevented from doing so, the surfactant will continue to impart its surface tension reducing properties on surrounding fluids and the environment even where it may be undesirable to do so.
This is especially true where the surfactant has been included or incorporated in the product for the purpose of lowering the surface tension of an insulting or contacting fluid. For example, in certain applications, especially in diapers, training pants and the like, where at least some of the surfactant passes from a topsheet or liner of the diaper or training pant to a second layer but is not inactivated or degraded, rewet or backflow of the fluid intended to be removed from the wear surface may occur to some degree, thereby reducing the effectiveness of the product and/or possibly causing leakage. Rewet or backflow is frequently the result of the pressure which is generated by the wearer""s actions (i.e. sitting, twisting, etc.) and by the remaining surface activity of the surfactant which has migrated into the product with the fluid (e.g. the surfactant""s surface activity inside the article reduces the surface tension of the fluid contained therein and allows or encourages the movement of fluid from inside the article back to the wear surface of the article, thereby defeating the original intent of containing the fluid in the article). The inability to inactivate or degrade a surfactant often reduces the effectiveness of the product, and especially personal care products. Furthermore, as above, the presence of an active surfactant in an absorbent material adversely effects the wicking properties or capillary action (as expressed by Laplace""s equation) of the material.
Although some surfactants are known to be degradable, such as those disclosed in U.S. Pat. No. 5,527,560 of Fereshtehkhou et al., U.S. Pat. No. 5,427,696 of Phan et al., U.S. Pat. No. 5,312,522 of Phan et al., and U.S. Pat. No. 5,274,159 of Pellerite et al., these surfactants typically are used as softeners and detergents. The use of pH degradable surfactants in personal care product applications is not known. Furthermore, the surfactants developed as detergents and softeners depend on temperature for their degradability characteristics that are due, presumptively in part, to the fact that a range of temperatures can be expected in the environment or in the environment they are intended to be used in, whereas a specific range of pH cannot be accurately controlled, projected or expected to occur in the environment. Those surfactants which are known to be pH degradable are used in water treatment stations; however, those surfactants do not degrade substantially immediately and are part of a homogeneous solution where the pH of the entire solution is substantially uniform. (See xe2x80x9cTRITON SP-Series Surfactantsxe2x80x9d pamphlet UC-1492, published by Union Carbide Corporation.) It is not known to use pH degradable surfactants in heterogeneous composites.
Thus, there is a need for a surfactant or class of surfactants which provides the desired wetting, spreading, emulsifying, dispersing, penetrating, and/or adhesion properties on the surface of the substrate to which the surfactant is applied, yet becomes inactivated or is degraded immediately upon or soon after contact with or passing into another layer or portion of the substrate. There is also a need for a method of degrading or inactivating a surfactant wherein the method is not temperature dependent. Additionally, there is a need for a method of inactivating or degrading a surfactant through the use of an acidic or a basic material, such that when a suitable surfactant and a suitable acidic or basic material are incorporated into a composite or product, the surfactant acts to lower the surface tension of a fluid on the surface of the product so as to allow or more readily enable the fluid (and some or all of the surfactant which is carried by the fluid) to pass into the substrate, and the acidic or basic material inactivates or degrades the surfactant upon or soon after contact therewith, such that the surfactant does not substantially adversely effect the desired wicking and absorption properties of the product.
In response to the discussed difficulties and problems encountered in the prior art a new method and composite for inactivating or degrading surfactants used in connection with personal care products have been discovered. The composite not only provides for acceptable wetting and penetration of the outer surface of a substrate by a fluid, but also provides for the inactivation or degradation of the surfactant enabling greater wetting and penetration of the substrate once the surfactant passes into a second layer of the substrate. Thus, the composite is able to realize the advantages and benefits of surfactants without experiencing the adverse effects typically associated with the use thereof.
Specifically, in the present invention, one or more surfactants are incorporated into an article or product for reducing the surface tension of the fluid contacting or insulting the wear surface of the product. That is, the surfactants are generally incorporated to promote wettability and penetrability of the substrate. In use, when a substrate surface having a surfactant applied thereto is contacted by a fluid, the surfactant lowers or reduces the surface tension of the fluid and allows or more readily enables fluid penetration of the outer surface of the substrate. While providing a reduction in the surface tension of the fluid on the surface of the substrate, a portion of the surfactant typically dissolves and moves with the fluid into the substrate or article, where the surfactant is degraded or inactivated upon or soon after passing into or contacting an inner portion of the article or a second layer of the substrate. Once the surfactant is inactivated, further handling of the fluid will be made easier in that the absorption and wicking properties of the second layer of the substrate will not be adversely effected. Furthermore, the concern of environmental contamination and the problem of rewet or backflow typically associated with surfactants in personal care products is significantly reduced. Additionally, for some applications, it is desired that the surfactant only be applied in the target zone or zones of the product or composite material. Applications which are limited to the target zone further reduce the amount of non-degraded or non-inactivated surfactant which is introduced in to the environment or other surroundings once the product is discarded or otherwise disposed of. That is, surfactant which might have been applied to the composite material, but which would not have passed into the second layer of the substrate, because a lack of contact with the contacting or insulting fluid, and which would otherwise have remained surface-active when introduced into the environment or other surroundings upon disposal will not get released into the surroundings at a later time where it might have a detrimental effect. Targeted application of the surfactant will also further reduce flowback or rewet concerns where the second layer of the substrate is not separated by an optional third layer (i.e. a second layer of a liner or a second surge layer).
The present invention relates to a composite material that includes a substrate, and a surfactant, wherein the substrate has at least a first layer and a second layer, the first layer having a first surface and a second surface, and wherein the surfactant is applied to the first layer of the substrate. The surfactant acts to lower the surface tension of a fluid which contacts the first layer of the substrate such that the contacting fluid is allowed or more readily enabled to pass through the first layer of the substrate, but such that the surfactant does not substantially adversely effect the absorption capacity or wicking height of the second layer of the substrate, as the second layer of the substrate substantially inactivates the surfactant. That is, once the surfactant passes through the first layer of the substrate, the surfactant is inactivated or degraded, or substantially so, such that the surface tension within the substrate increases thereby encouraging the fluid to pass into or through the second layer of the substrate. To enhance absorption of the composite material, it is contemplated that the second layer of the substrate is or comprises an absorbent core, such as a superabsorbent material or pulp. It is also contemplated that the second layer of the substrate is basic or acidic, in that upon contact with the second layer of the substrate, the fluid will have a pH in the range from about 1 to about, but not equal to, 7, more desirably from about 2 to about 6, and most desirably from about 3 to about 5. Alternatively, the second layer of the substrate may be basic having a pH in the range from about, but not equal to, 7 to about 14, more desirably from about 8 to about 12, and most desirably from about 9 to about 11. Although not limited thereto, the surfactant applied to the substrate is desirably chosen from the a class of surfactants having a disulfide bond, a ketal group or a siloxal group.
The present invention is further directed to a composite material including a substrate and a surfactant, the substrate having at least a first layer and a second layer, the first layer having a first surface and a second surface, the surfactant being applied to the first layer of the substrate. The composite material has properties such that when a fluid having a first surface tension contacts the first layer of the substrate, the surfactant acts to lower the surface tension of the fluid to a second surface tension, so as to permit or more readily enable the fluid to pass through the first layer of the substrate. Once the fluid having a reduced surface tension has passed through the first layer and into the second layer of the substrate, the surfactant in the substrate begins to inactivate or degrade causing the surface tension of the fluid in the substrate to increase to a third surface tension. In this embodiment it is desired that at a time 24 hours after the fluid having the first surface tension contacts the surfactant, the third surface tension of the fluid is at least 5 dynes/cm greater than the lowest second surface tension which is experienced by the fluid, more desirably at least 10 dynes/cm greater than the lowest second surface tension experienced by the fluid, more desirably at least 20 dynes/cm greater than the lowest second surface tension experienced by the fluid, and most desirably at least 30 dynes/cm greater than the lowest second surface tension experienced by the fluid. As with the other embodiments of the present invention described above, this substrate of this embodiment may be selected from woven fabrics, knit fabrics, nonwoven fabrics, foams, film-like materials and paper materials. It is further contemplated that the composite material of this embodiment may comprise a personal care product or component thereof, as well as a sorbent, wiper, or component thereof, or the like.
The invention is also directed to a method for forming a composite material adapted for inactivating surfactants upon contact with a portion of a substrate. The method includes providing a substrate having at least a first layer and a second layer, applying a surfactant to the first layer of the substrate, and subjecting the substrate to at least one condition which facilitates migration of the surfactant from the first layer of the substrate to the second layer of the substrate. The alkalinity of the second layer of the substrate is non-neutral such that the non-neutral layer reacts with any of the surfactant which comes in contact therewith, such that the absorption and wicking properties of the second layer of the substrate are not substantially adversely effected by the surfactant. The alkalinity of the second layer may range in pH from about 1 to about 14, except that the pH of the second layer should not be equal to 7. The desired surfactants include, but are not limited to, those having a disulfide bond or containing a ketal or siloxal group.
The invention is also directed to a method of degrading or inactivating a surfactant once the surfactant has changed the surface tension of the contacting fluid and passed into the substrate. The method includes the provision of a substrate having at least two layers, applying a surfactant to the first layer of the substrate, insulting the first layer of the substrate with a fluid, lowering the surface tension of the fluid contacting the first layer of the substrate, allowing or more readily enabling the fluid and at least a portion of the surfactant to pass through the first layer of the substrate into the second layer of the substrate, and inactivating the surfactant when or soon after the surfactant passes into or comes in contact with the second layer of the substrate.
It is contemplated that the substrate of the composite material and methods described herein may comprise a sorbent product, a personal care product, a wiper, or one or more components thereof.
With the foregoing in mind, it is a feature and advantage of the invention to provide a composite material which has a surfactant that sufficiently reduces the surface tension of an insulting or contacting fluid so that the desired penetration of the outer surface of the composite is achieved, yet does not substantially adversely effect the desired absorption, wicking and wetting characteristics of the other layers of the substrate.
It is also a feature and advantage of the invention to provide a method of rapidly degrading or inactivating a surfactant once it has changed the surface tension of a fluid and passed into the article which the composite material comprises.